1. Field of the Invention
This invention relates to a method for the reprocessing by oxidation of condensate obtained in urea production plants and having a urea content in the order of 50 mg/l and of biuret in the order of 2 mg/l.
2. Description of the Prior Art
Condensate obtained in chemical process plants constitutes a byproduct and is generally too valuable for being discharged as waste fluid.
The production of urea, (NH.sub.2).sub.2 CO.sub.4 H.sub.2 O, yields a byproduct condensate which contains as impurities up to 200 mg/l of urea and 5 mg/l of biuret. A substantial portion of these impurities can be expelled by boiling to reduce, for example, the urea content to approximately 50 mg/l and the biuret content to about 2 mg/l. This partially purified condensate can be used as feedwater for low-pressure steam boilers.
Modern urea production plants are part of a chemical complex in which heat of reaction is recovered at preferably high operating pressure levels of, for example, 80 to 130 bar, for steam generation in high-pressure steam boilers. Because of the large quantities of reaction heat liberated in large-scale chemical plants, the demand for high-quality boiler feedwater is considerable; therefore, reprocessing of all condensate should be aimed at.
It is also known to convert by oxidation the major portion of the impurities, i.e. urea and biuret, to nitrogen and carbon dioxide with the aid of oxidizing agents such as hypobromite, sodium hypochlorite or nitrous acid. However, this method is unsatisfactory because complete oxidation cannot be achieved at low residual concentrations.